I had to look up what a cloche hat was, and then felt silly because I own one and just didn't know what they were called! I have to say, while I think it would be possible to bring that hat on a ride and hold it in my hands, it's not something I would personally take on rides since I'd be afraid of it getting crushed (and it absolutely would not stay on my head). Also would not want to have to worry about white silk pants on potentially dirty ride seats, or about potential snags on uneven surfaces. So I guess my general thought is that I personally would not do it.
Are you only going to be at MK for the Christmas party? Or will you have other park time there? Anymore it seems like the Christmas party doesn't have particularly short times for rides, so what I would suggest would be to, as others have suggested, get a locker and plan on changing your clothes. If you're able to go to the park earlier in the day you could wear something a bit more durable then and get all your rides in, then change into the fancy clothes at party time and spend the evening focusing on photos, parades, and all the other non-ride things the party offers.